In recent years, electronic devices are becoming highly-integrated, sophisticated, and miniaturized. There has been promoted thermal analysis for estimating or confirming the effect of heat release by using a thermal analysis model that a heat releasing (heat generating) condition of a printed-circuit board or an electronic component mounted on the printed-circuit board, etc. in such an electronic device is modeled.
For example, there is known a thermal analysis model for calculating a physical property value of a printed-circuit board by using the number of wiring layers (the number of layers) of the printed-circuit board, the thickness of wiring layers of the printed-circuit board, an area ratio (an occupancy rate) of a wiring pattern to the printed-circuit board, and the thickness of the entire printed-circuit board as parameters. Specifically, two components: an effective thermal conductivity of the printed-circuit board in a horizontal direction (a plane direction) and an effective thermal conductivity of the printed-circuit board in a vertical direction (a layer direction) are calculated as physical property values.
As an example, when an area of the printed-circuit board on which electronic component(s) can be mounted is denoted by S [m2] and copper foil (wiring information) is denoted by Cu [m2], a residual rate of copper foil is Cu/S (%). As a result of generation of this thermal analysis model, a physical property value can be expressed by “equivalent thermal conductivity=thermal conductivity of copper×(Cu/S)”.
A concrete example is described with reference to FIG. 12. FIG. 12 is a diagram for explaining thermal analysis modeling. A printed-circuit board 200 illustrated in FIG. 12 includes an electronic component 201, a pattern 202, an electronic component 203, and an electronic component 204. When a thermal analysis model is generated from the printed-circuit board 200 by the technique described above, it is modeled as one conductor 300 having an “equivalent thermal conductivity” as illustrated in FIG. 12.
Furthermore, there is known a thermal analysis model for dividing a printed-circuit board into arbitrary grids, calculating an area ratio of copper foil in each grid, and calculating a thermal conductivity of each grid. In this technique, if thermal conductivities of adjacent grids are an equal value, the grids are integrated, thereby preventing the thermal analysis model from being large in scale.    Patent document 1: Japanese Laid-open Patent Publication No. 11-066122    Patent document 2: Japanese Laid-open Patent Publication No. 2010-134497
However, there is a problem that thermal analysis using a physical property value calculated based on a conventional thermal analysis model is low in accuracy of analysis. For example, a thermal conductivity calculated as a physical property value based on the conventional thermal analysis model is an average value of an entire printed-circuit board. However, in an actual printed-circuit board, a thermal conductivity is not constant, and different thermal conductivities are distributed locally. Therefore, even if thermal analysis is conducted using the average thermal conductivity of the entire printed-circuit board, the accuracy of analysis is not high.
Furthermore, the accuracy of analysis may be increased by reducing the size of grids into which the printed-circuit board is divided; however, in this case, as the size of grids gets smaller, a larger-scale thermal analysis model is generated and therefore it takes a longer time to analyze in the thermal analysis, so it is not practical.